The 50.0.1 vulnerability was introduced in 49, which is why 45 didn't need an update to fix it.

45 did include the 50.0.2 vulnerability, which is why 45.5.1 was released. So 50.0.2 and 45.5.1 both fix the same vulnerability and there won't be a 45.5.2 unless another vulnerability is uncovered before 45.6.0 comes out.